doi:10.1038/nindia.2018.4 Published online 15 January 2018
"I managed to catch a glimpse of its tail."
"I saw its shadow."
"Lucky if you spot one!"
This excitement among tourists at the Keibul Lamjao National Park (KLNP) — the world's only floating reserve — in the north east Indian state of Manipur is rather usual. The buzz is around the endangered and elusive Sangai or the Indian Eld's deer (Rucervus eldii eldii), locally called the "dancing deer" for its dainty gait.
However, the Sangai, Manipur's state animal and a leitmotif of the state's art, culture and folklore, is now critically threatened by untreated human waste that is making its way into the 40 square kilometre national park, the deer's last refuge. Liquid effluents, solid wastes and sewage from Manipur's capital city Imphal are invading the deer's abode through polluted rivers that empty into the national park.
Added to that, loss of genetic variability, inbreeding, genetic drift and catastrophic events like flood and diseases have rendered the animal critically endangered. Sangai is also included in Appendix 1 of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). The deer was actually thought to have gone extinct until a remnant population was rediscovered in 1950 at the south-eastern fringe of Manipur's Loktak lake.
KLNP is the protected southern rim of the iconic saucer-shaped freshwater lake Loktak, and is about a quarter of the size of Assam's famous Kaziranga National Park. The swampy Loktak, once the lifeline for people in the Manipur Valley, is famous for the phumdis — squelchy masses of vegetation, soil and organic matter buttressed together in various stages of decomposition — to form the floating meadows for the Sangai. It is the largest freshwater lake in northeast India, straddling the Barak-Chindwin river basin in the Indo-Myanmar border.
A 90-minute drive from Imphal gets one to Sendra, the highest point of the lake that offers a bird's eye-view of the phumdis dotting the water body — beautiful rings of green stretching across the clear blue expanse of the lake. These floating meadows take up to 20 years to form and collectively house around 260 deer, whose elegant gait inspires Manipuri dance moves and much of its folklore.
The islets are thinning due to water pollution and untreated waste, making it tough for the deer to survive. About 65 per cent (26 square kilometre) of the national park is covered with a thick and almost contiguous mat of floating meadows.
"To support the weight of Sangai (each weighing between 90 and 150 kg) and sustain a stable population, the phumdis need to be at least a metre thick," says Chongpi Tuboi of the Wildlife Institute of India (WII). Tuboi, a project scientist, in WII's conservation action plan for Sangai, says phumdis of recent origin are less than a metre thick. "Only about nine square kilometres of the total park area has the desired phumdi thickness," she points out.
Loktak's water woes are mainly due to loss of vegetation cover in its catchment and construction of a barrage on the lake's southern side. Poor water quality has altered the vegetation cover and composition of the phumdis and hence their potential to sustain the Sangais. The construction of the Ithai Barrage in 1983 has impacted the lake's natural flushing mechanism.
"The lake was a seasonally flooded wetland with several small wetlands that separated during dry season and merged in monsoon," Tuboi explains. After the construction of the barrage, the water level in the lake is maintained at a regular 769.12 metres above mean sea level so as to support the hydro-power project. Tuboi says the lake is under stress due to "permanent flooding". This does not allow the phumdis to settle on the water bed during dry season or to pick up nutrients and soil to maintain the desired thickness.
Tuboi and colleagues Syed Ainul Hussain and Michelle Irengbam tested1 water samples for three consecutive years (2008 to 2010) across 11 sites of the wetland, which is fed by around 30 rivers and streams, including the highly polluted Nambul and Nambol rivers.The Ithai Barrage is the only outlet for this lake. Both liquid effluents and solid wastes discharged from Imphal are drained directly into Loktak via the Nambul river.
They found that Loktak lake was "severely polluted" due to the influx of sewage and other wastes from these two rivers. In addition, surface runoff from the surrounding agricultural and catchment areas was also diminishing the lake's water quality, indicated by the high nitrogen concentration.
The researchers recommend setting up sewage treatment plants at strategic locations, such as at the inlet channel at Toubul village, which is surrounded by the lake. Meanwhile, Tuboi and his team have been surveying spots within the lake where a satellite population of the Sangai could be relocated.
"Sangai is the flagship species. If we save it, we save everything else. Before the fragile balance between the lake ecosystem and the local cultural practices is permanently lost, the lake needs to be restored by improving its water quality and hydrological regime," Tuboi added.
Hope for the Sangai was recently rekindled when a team of researchers from Hyderabad-based Centre for Cellular and Molecular Biology (CCMB) sequenced the deer's complete mitochondrial genome2. “The mitogenome sequence tells us that it is genetically distinct from other subspecies owing to its geographic isolation,” says Ajay Gaur, a principal scientists at CCMB's Laboratory for Conservation of Endangered Species (LaCONES).
Gaur and his colleagues took a crack at the Sangai mitochondrial DNA from a tissue sample and reported the 16, 357 base pair long mitogenome. A mitogenome analysis helps in comparing closely related organisms. Using several unique characteristics like maternal inheritance, high evolutionary rates, small genome size, conserved gene content, and lack of extensive recombination of mitochondrial genes, scientists use such sequences to track the evolutionary history of the animal and its speciation.
Armed with the new genetic insights that clearly distinguish it from its close cousins, Gaur advocates a 'distinct conservation status' for Sangai. "What we can say from our study is that the population needs to be stabilised. Despite the fact that the subspecies had a common ancestor, you can’t treat all populations (of the Eld’s deer) the same. Conservation practices need to be customised as per the specific geographical population."
It is common conservation practice to create alternate homes for isolated, single-population species so that they are not wiped off from the face of earth if an epidemic or natural disaster strikes. The Manipur government is considering a proposal by its forest department to shift the species to a nearby fresh water lake Pumlenpat , the second largest in the state after Loktak, also replete with phumdis. However, this lake also faces unique challenges due to human settlements and encroachment, and it will be long before livelihood issues for local fisher folks are solved.
Till such time, the vulnerable floating meadows remain the Sangai's only home on earth.
[This article has been published with support from the TransDisciplinary University (TDU)-Nature India Media Fellowship in Science Journalism. The author can be contacted at email@example.com]
1. Tuboi, C. et al. Seasonal variations in the water quality of a tropical wetland dominated by floating meadows and its implication for conservation of Ramsar wetlands. Phy. Chem. Earth Pt. B. (2017) doi: 10.1016/j.pce.2017.09.001
2. Tabasum, W. et al. The complete mitochondrial genome of Eld's deer (Rucervus eldii eldii) and its phylogenetic implications. Gene Reports. 9. doi: 10.1016/j.genrep.2017.10.001